Resistance to melon vine decline derived from Cucumis melo ssp. agrestis: genetic analysis of root structure and root response

Melon vine decline is a major soilborne disease that causes severe economic losses around the world. The fungal pathogens Monosporascus cannonballus Pollack et Uecker and Acremonium cucurbitacearum Alfaro‐García, W. Gams et J. García‐Jiménez have been reported as the main causal agents of this disease. A relatively high level of resistance has been reported in Cucumis melo L. ssp. agrestis (Naud.) Pangalo in the Asiatic accession Pat 81. Although specific resistance mechanisms controlling pathogen‐induced root lesions have been characterized in Pat 81, the development of a vigorous and branched root system can also appreciably increase its tolerance to vine collapse. The genetics of root traits related to root vigour and structure were studied in the progeny derived from a cross between Pat 81 and the highly susceptible cultivar ‘Piñonet’ market class ‘Piel de Sapo’(C. melo L. ssp. melo). The inheritance of specific resistance to soilborne fungi was also studied by analysing root response to inoculation employing naturally infested soil. Estimates of the broad‐(H) and narrow‐sense (h²) heritabilities indicated that the majority of the variation for lesion resistance in lateral and fine roots, in the root weight, root length, and the root surface area could be explained by additive effects, whereas dominance is important in plant biomass and resistance to lesions in hypocotyls. Selection for improved root systems conferring resistance and tolerance to vine decline was successfully conducted in BC₁ progeny derived from a Pat 81 בPiñonet’ mating. Moderate values of heritabilities (0.03–0.76) suggest that breeding strategies that combine family and individual selection could enhance genetic progress. As some of the traits analysed exhibited heterosis, breeding methods directed towards recovering hybrid vigour may increase gain from selection.     

Genetic Variability in Phosphorus Acquisition and Utilization Efficiency from Sparingly Soluble P-Sources by Brassica Cultivars under P-Stress Environment

Plants display an array of classical strategies to maximize phosphate (Pi) acquisition from sparingly soluble P sources. Acclimation to Pi-stress via elegant Pi-starvation induced (PSI) adjustments would reduce our current overreliance on expensive, polluting and non-renewable Pi-fertilizers. Nevertheless, differences in the ability of various species to solubilize sparingly soluble P-sources have been often evidenced; inter-cultivar variations are scarcely documented. Brassica is known as an effective, non-mycorrhizal user of sparingly soluble P-sources. Various growth parameters and biomass accumulation by genetically diverse Brassica cultivars were determined in four experiments using hydroponics and quartz sand culture media. Role of PSI root mediated pH changes, organic anions (OAs) exudation and altered root architecture in mobilization and acquisition of sparingly soluble P-forms [Jordan rock-P (RP) at 2 g l⁻¹ and Ca₃(PO₄)₂ (TCP) at 0.2 g l⁻¹ respectively] was investigated. Cultivars showed considerable genetic variations in biomass accumulation, various growth parameters and root–shoot ratio. Concentration and total uptake of P, specific absorption rate of P, P-transport rate and P-utilization efficiency (PUE) were also significantly (P < 0.001) different for various cultivars and their dry matter was significantly correlated with P-uptake [r = 0.94** (significant at 1% level)]. P-tolerant cultivars showed substantial decrease in solution media pH because of H⁺ efflux and exuded more carboxylates than low P-sensitive cultivars under P-starvation. P-uptake by cultivars increased linearly with decreasing pH. The amount and types of OAs exuded from the roots of P-starved plants differed from those of plants grown under P-sufficient environment. In split pot study, with TCP and RP supplied spatially separated from other nutrients, efficient cultivars were still able to mobilize RP and TCP more efficiently than inefficient cultivars. In rhizobox study, the elongation rates of primary roots decreased but the elongation rates of the branched zones of primary roots and the length of lateral roots increased under P-starvation. Tested cultivars showed genetic diversity in accessing, mobilization, acquisition and utilization of Pi from sparingly soluble P forms. An arrange marriage of plant traits can explain cultivar’s access to different forms of sparingly soluble P, and in addition to altered lateral root topology and enhanced P-uptake and PUE, enhanced H⁺ efflux and OAs exudation are key factors in Pi scavenging from extra cellular sparingly soluble P-forms.     

Sources of resistance to diseases of sugar beet in related <Emphasis Type="Italic">Beta</Emphasis> germplasm: I. Foliar diseases

Resistance to four foliar diseases of sugar beet (Beta vulgaris ssp. vulgaris), virus yellows caused by Beet mild yellowing virus (BMYV) and Beet yellows virus (BYV), powdery mildew (Erysiphe betae) and Cercospora leaf spot (Cercospora beticola), was assessed in up to 600 accessions of closely related wild and cultivated Beta species. Most accessions were from the Section Beta, a taxon containing types most closely related to, and sexually compatible with, sugar beet and therefore most valuable for use in crop improvement. Between 1–12% of accessions were highly resistant (resistance scores of 2 on an international standardised resistance scale of 1–9) to these diseases. These levels, however, underestimate the potential number of resistant sources available from this section as some accessions with intermediate mean resistance scores contained a significant proportion of highly resistant plants within segregating populations. Variation in resistance to all diseases except BYV was observed within the Section Beta. Much higher levels of resistance were observed, and more frequently, in more distantly related sections of the genus Beta. Accessions of the Section Corollinae were highly resistant to both viruses (>62% of accessions tested), but less so to Cercospora (15%) and they were very susceptible to powdery mildew. Section Procumbentes accessions were highly resistant to BMYV and Cercospora (100%) but less so to powdery mildew (50%) and BYV (20%). However, sexual incompatibility between these sections and sugar beet make utilisation of these sources impractical using conventional breeding methods.     

Genetic variability in melon based on microsatellite variation

A set of 18 simple‐sequence repeat (SSR or microsatellite) markers was used to study genetic diversity in a collection of 27 melon (Cucumis melo L.) accessions, representing a broad range of wild and cultivated melons. The materials studied were highly polymorphic for SSRs and a total of 114 alleles were detected (average of 6.3 alleles per locus). Cluster analysis suggests the division of these accessions into two major groups, largely corresponding to the division of C. melo in the two subspecies agrestis and melo. The assignment of the accession to the subspecies was generally in agreement with published reports, except for those corresponding to the ‘dudaim’ and ‘chito’ cultivar groups, which, according to the observed SSR variability, should be included in subspecies agrestis. Based on cluster analysis, five groups of accessions were defined. The two most divergent groups include mainly accessions from the Mediterranean which form one group, and accessions from China, Japan, Korea and India forming the other. Both groups shared a low level of intra‐accession variation compared with the other groups, which suggests an erosion of their genetic variability because of drift and/or inbreeding. The remaining accessions, mainly from Central Africa and India, were more variable and may be an important source of genetic variation for melon breeding.     

Geographical differentiation and diallel analysis of seed dormancy in barley

Seed dormancy is one of the most important parameters affecting the malting process and pre-harvest sprouting in barley (Hordeum vulgare L.). Variation of seed dormancy in 4365 cultivated and 177 wild barley (ssp. spontaneum) accessions derived from different regions of the world was investigated in Okayama University, Kurashiki, Japan. Seed dormancy of each accession was estimated from their germination percentages at 0, 5, 10 and 15 weeks post-harvest after-ripening periods. All of the wild barley accessions showed less than 10% germination at 0 week after-ripening period. Level of seed dormancy in 4365 cultivated barley accessions showed a clear geographical differentiation. Seventy seven percent of Ethiopian accessions showed high germination percentages, while 86% of Japanese, Turkish and North African accessions showed low germination percentages at 0 week after-ripening period. A half diallel cross using eleven barley accessions with different level of dormancy revealed that seed dormancy was predominately controlled by additive gene effects. These results suggest that large genetic diversity for seed dormancy in barley is explained as different levels of additive accumulation of genetic factors. Barley varieties showing appropriate dormancy could be developed by crossing among barley germplasm accessions used in the present study.     

Reaction of wild species of the geneus Lens to drought

Summary Susceptibility to drought stress is a key factor in dry land lentil (Lens culinaris Medikus) production in the Mediterranean region of West Asia and North Africa. This study examined the response to drought stress of 121 accessions representing all subspecies of the genus Lens; cultivated, and the wild L. culinaris ssp. orientalis (Boiss.) Ponert, L. culinaris ssp. odemensis (Ladiz.), L. nigricans M.B. Godr. ssp. nigricans Godr. and L. nigricans ssp. ervoides (Brign.) Ladiz. for their potential use in breeding for dry land conditions. Accessions were grown under two moisture regimes (dry land and dry land plus supplemental irrigation) at Breda, Syria during the 1990–91 and 1991–92 seasons. The cultivated lentil had markedly superior seed and straw production than did the wild Lens species. Time to flowering accounted for less than 10% of the variation in yield of wild accessions under rainfed conditions in the two seasons, showing that, in contrast to the cultivated germplasm, drought escape was relatively unimportant in wild lentil. Performance under drought in wild lentil, measured in terms of dry land seed yield or drought susceptibility index (S), was randomly distributed among collection locations with little relation to collection site aridity. Direct selection of wild lentil germplasm for biomass yield under dry conditions is of little value and an evaluation of wild accessions in hybrid combination is needed.     

Resistance to the cabbage root fly, <Emphasis Type="Italic">Delia radicum</Emphasis> (Diptera,Anthomyiidae), of turnip varieties (<Emphasis Type="Italic">Brassica rapa</Emphasis> subsp. <Emphasis Type="Italic">rapa</Emphasis>)

The cabbage root fly Delia radicum L. (Diptera: Anthomyiidae) is one of the major pests of many Brassica crops in the temperate areas of Europe and North America. At present, turnip (B. rapa ssp. rapa L.) varieties resistant to the pest does not exist. With the aim to fill this gap, a no-choice tolerance test of 56 accessions among turnips, turnip tops and turnip greens was performed under controlled conditions by introducing D. radicum eggs. Plant survival, leaf and root conditions, pupae number and weight significantly varied among plant accessions. Ten putatively resistant and ten susceptible accessions (control group) were selected from this first screening, transplanted in the field and exposed to natural infestation to detect antibiosis and antixenosis mechanisms. Both in the laboratory and in the field, pupae number significantly varied within accessions and between resistant and susceptible group, although pupal weight did not, indicating the absence of antibiosis effect on this early stage. In the field, the number of galleries was significantly lower in the resistant group in comparison with the control. Resistant accessions had smaller size, and a smaller, white and mostly buried root. Within the resistant and susceptible accessions, larger plants harboured more pupae, however purple roots were those most preferred, and the hosted pupae weighed most. Three accessions from the resistant group (MBGBR0178, MBGBR0570 and MBGBR0371) stand out for resistance to D. radicum possibly through antixenosis mechanisms.     

Determination of genetic variation and taxonomy in lentil (Lens Miller) species by chloroplast DNA polymorphism

Summary Chloroplast DNA restriction fragment lenght polymorphisms (RFLP) were used to examine the taxonomic relationships of cultivated and wild lentil (Lens Miller) species and identify the extent of genetic variation in this genus. Twelve accessions representing all Lens subspecies were digested with four hexanucleotide-recognizing restriction endonucleases. These digests randomly surveyed 540 base pairs, or 0.4% of the approximately 125 kilobase lentil chloroplast genome. A high degree of gragment length conservation was seen among members of crossability group I, i.e., L. c. ssp. culinaris, L. c. ssp. orientalis and L. c. ssp. odemensis. Accessions of the two subspecies comprising crossability group II, i.e., L. n. ssp. nigricans and L. n. ssp. ervoides, showed the greatest amount of variation when compared to the cultivated lentil, L. c. ssp. culinaris. Limited variation was observed within subspecies except for L. n. ssp. nigricans, where accessions of the normal cytotype were highly polymorphic to those of the differentiated cytotype. Chloroplast DNA RFLPs reaffirm hypotheses that propose L. c. ssp. orientalis as the progenitor to the cultivated lentil. The implications of this study on taxonomy and genetic resources is also discussed.     

Evaluation of genetic diversity and root traits of sea beet accessions of the Adriatic Sea coast

Thirty-nine sea beet [Beta vulgaris L. ssp. maritima (L.) Arcang.] accessions of the Adriatic coast were screened genetically and for their adaptive morpho-functional root traits in order to identify new sources of abiotic resistances for sugar beet breeding programs. Genetic diversity was evaluated with 21 microsatellites markers that identified 44 polymorphic alleles. Sea beets grouped into two main clusters: the West and the East Adriatic coast groups, with the latter showing higher genetic diversity. Among sea beet accessions with desirable root traits, four accessions have proved to be interesting for sugar beet [B. vulgaris (L.) ssp. vulgaris] breeding aimed to improve tolerance to nutritional stresses. Lastovo (ID 29) and Zut (ID 34) accessions were characterized by the highest values of RER, TRL, FRL and RSA still maintaining a high value of RTD, while Grado (ID 21) an Portic (ID 23) accessions were characterized by the highest RTD, but with low values of RER, TRL, FRL and RSA parameters.     

Response to Mycosphaerella pinodes in a germplasm collection of Pisum spp

Little resistance against Mycosphaerella pinodes is available in pea. In this work 78 accessions of Pisum were screened for resistance to M. pinodes. Fourteen accessions showed a good level of resistance in seedlings under controlled conditions, and in mature plants in the field. The highest levels of resistance were found in P. fuivum, followed by P. sativum ssp. eiatius and P. sativum ssp. syriacum. Resistance of five selected accessions was effective against different isolates of M. pinodes originating from different countries. Resistant accessions reported in this paper have been successfully hybridized with field pea cultivars.     

Beet mild yellowing virus resistance derived from wild and cultivated Beta germplasm

Sugar beet (Beta vulgaris ssp. vulgaris L.) has a relatively narrow genetic base and several programmes have sought to evaluate the potential for introducing novel traits from wild and cultivated Beta germplasm into the crop. In particular, resistance to important sugar beet diseases has been identified within individual Beta accessions. We report here the successful transfer of resistance to Beet mild yellowing virus (BMYV) from garden beet, fodder beet and leaf beet accessions to progeny populations in initial crosses with sugar beet. Twelve plant populations derived from different Beta accessions were inoculated with viruliferous aphids carrying BMYV and the virus content of individual plants subsequently quantified by an ELISA test. Seven populations were significantly more resistant than a control sugar beet cultivar (P ≤ 0.05). BMYV resistance was successfully inherited in BC₁ and BC₂ generations, suggesting that resistance could potentially be introgressed from these sources into elite sugar beet lines.     

Seed colour, seed weight and seed oil content in Linum usitatissimum accessions held by Plant Gene Resources of Canada

The purpose of this study was to investigate variation of and relationships among seed colour, seed weight and seed oil content in cultivated flax (Linum usitatissimum L. ssp. usitatissimum). Seed from 2934 flax genebank accessions recently grown at Saskatoon, SK, Canada, originating from 72 countries was used to describe the variation of the seed characters. The dominant seed colour of the accessions was medium brown (2730 accessions, 93.0%), followed by yellow (126 accessions, 4.3%). Based on single observations for all accessions, the overall mean and standard deviation was 5.95 ± 1.22 mg/seed for seed weight and 38.3 ± 1.74% for oil concentration. Within three infraspecific groups of flax, seed weight, oil concentration and oil amount per seed increased in the following order: fibre flax (convar. elongatum), intermediate flax (convar. usitatissimum), large‐seeded flax (convar. mediterraneum). The world collection exceeded the range of variation of seed weight and oil concentration found in 52 North American cultivars. There was a weak, positive association of higher oil concentration with higher seed weight (r² = 0.32; P < 0.001). Yellow‐seeded flax had a higher seed weight (6.31 vs. 5.92 mg/seed) and oil concentration (39.4% vs. 38.3%) than brown‐seeded flax. There was a tendency for yellow seed colour to be associated with higher oil concentration in all seed weight classes. The results suggested that indirect selection for increased seed oil concentration in flax is possible by selection for higher seed weight and yellow seed colour.     

Progress in improving aluminium tolerance in the perennial grass,phalaris

Aluminium (Al) tolerance of 11 cultivars, breeding populations and accessions of the perennial grass, phalaris (Phalaris aquatica L.), was investigated in low ionic strength nutrient solutions. The populations were chosen to determine whether a program to improve the tolerance of phalaris to acid soils had resulted in improved Al tolerance. Populations derived by backcrossing genes from a more Al-tolerant species, P. arundinacea L. (AT populations), were significantly more Al tolerant than populations based on pure P. aquatica. Smaller levels of improvement in Al tolerance had also been achieved within P. aquatica through a combination of selection in Al solutions and at acid soil field sites. The response of roots and shoots to Al stress was similar. Some differences in ranking were obtained depending on whether Al tolerance was defined by actual growth in Al solution or growth relative to the zero Al treatment. Performance in nutrient solution containing Al was highly correlated with second year yield and persistence at a field site with acid soil high in Al to depth. Actual root dry weight in nutrient solution containing Al gave a slightly higher correlation with the field data than root weight relative to the zero control. A tendency for root dry weight to segregate in the presence of Al was observed in some P. aquatica populations but not in the AT populations. It was concluded that a significant improvement in the Al tolerance of phalaris has been achieved through a program to introgress genes from P. arundinacea into P. aquatica.     

Agronomical performance and breeding value of selected strains of diploid wheat,Triticum monococcum

Summary Twenty-one germplasm accessions and breeding lines of einkorn wheat (Triticum monococcum ssp. monococcum and ssp. sinskajae) were grown at two sites in Italy and evaluated for various field and seed characteristics. Grain yields of germplasm accessions were relatively high (317–3238 kg/ha), but distinctly lower than those of four modern cultivars of tetraploid (T. turgidum ssp. durum) and hexaploid wheat (T. aestivum ssp. Aestivum) included in the experiments as controls. As expected, all Einkorns-including some substantially higher yielding crossbred lines (3415–4362 kg/ha)-were defective for one or more agronomically relevant features. However, a few of the accessions examined were found to contain, as a group, practically all the genes needed to breed monococcums having the main field attributes of a modern wheat cultivar: high yielding capacity, good threshability, large kernel size, earliness, short stature and adequate lodging resistance. Still higher yielding diploid wheats, more responsive to improved growing conditions and of better seed quality, could probably be obtained from crosses with wild monococcums bearing mostly two-seeded florets and with accessions producing less slender-shaped kernels. Some of the Einkorns examined were found to carry minor genes for easy threshing which might enhance the efficacy of the major gene for soft glumes carried by T. monococcum ssp. sinskajae, a partially free-threshing diploid wheat taxon. Seed protein percentage of monococcums was markedly higher than that of durum and bread wheat cultivars even in those cases where their grain yields surpassed those of the polyploid checks. The possibilities offered by diploid wheat in the exploitation of novel endosperm mutants and F₁ hybrid vigour, as well as in the fields of celiac disease, crop diversification and resistance to agro-biological stresses are discussed. Breeding priorities and strategies are also proposed.     

Phylogenetic relationships in the genus Arachis based on seed protein profiles

Summary Seed protein profiles of 19 accessions representing seven sections of the genus Arachis were studied using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The general profile showed appreciable homology between these taxa, supporting their classification based on morphology and cross-compatibility relationships. The accessions of section Arachis expressed a high variation confirming inferences from earlier studies. Variation between accessions of a species is limited. Accessions of the section Ambinervosae and Caulorhizae formed one cluster and accessions of sect. Erectoides and Procumbensae formed another. Whereas the representative accessions of sect. Triseminalae and Extranervosae formed two independent clusters. Using the percentage of dissimilarity in electrophoretic bands as a statistical genetic distance between accessions, sect. Arachis (containing the cultivated groundnut, A. hypogaea) is phylogenetically closest to sect. Erectoides followed by Procumbensae, Ambinervosae, Caulorhizae, Triseminalae and Extranervosae, respectively.Submitted as Journal Article No. 1485 by the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) Patancheru, A.P. 502 324, India.     

Widening the gene pool of cultivated lentils through introgression of alien chromatin from wild Lens subspecies

Wild Lens species/subspecies are a potential source for increasing genetic diversity in cultivated lentil. Four intraspecific crosses were attempted between cultivated and wild lentils. Viable hybrids were produced between L. culinaris ssp. culinaris × L. culinaris ssp. orientalis and L. culinaris ssp. culinaris × L. culinaris ssp. odomensis. Normal meiosis and pollen fertility were observed in the first set of crosses, whereas chromosomal abnormalities and reduced pollen fertility were observed in the second set of crosses. These crosses were also studied for some quantitative traits. The range, mean and coefficient of variation were calculated in parents, F₁, F₂ and BC₁ generations to determine the extent of variability generated in the cultivated lentil through introgression of genes from wild lentil. The cultivated lentil × L. culinaris ssp. orientalis crosses showed substantially higher variability for all the traits than crosses involving cultivated lentil ×L. culinaris ssp. odomensis. The results of the present study indicated that these wild subspecies can be exploited for breeding purposes and their variation can easily be utilized to widen the genetic base of the cultivated lentil.     

Wild Oryza species as potential sources of drought-adaptive traits

Wild species of Oryza may serve as sources of superior drought tolerance alleles for cultivated rice. In a series of three screenhouse experiments, we compared traits associated with leaf water status, stomatal conductance, membrane stability, and root development in several wild Oryza accessions and O. sativa cultivars, when grown under well-watered or water-deficient conditions. One accession of O. longistaminata had greater stomatal conductance under stress and maintained leaf elongation better under stress than most other genotypes. Several upland-rice cultivars from the japonica subspecies also maintained greater conductance and leaf expansion than an indica cultivar or O. rufipogon accessions. Leaves of an accession of O. latifolia were particularly sensitive to water deficit. Oryza longistaminata and several O. rufipogon accessions had greater membrane stability, measured as electrolyte leakage from leaf disks after heat treatment, than cultivated rice. Drought treatments tended to reduce the levels of electrolyte leakage observed. Wild species had levels of osmotic adjustment under stress that were similar to O. sativa. Entries differed in the growth of roots with water deficit:O. longistaminata accessions and some japonica cultivars showed either an increase in total root mass or an increase in the proportion of root mass in deeper soil levels when water deficit was imposed, whereas indica cultivars and O. rufipogon accessions did not. Changes in root mass and distribution were correlated with values of stomatal conductance and leaf elongation; this suggests that leaf measurements made at key times in the drying cycle may reveal possible genetic differences in rooting behavior, which are otherwise difficult to measure. These studies indicate that O. longistaminata and O. rufipogon may serve as sources of novel alleles for improved leaf traits under drought stress–specifically, for maintenance of leaf elongation, stomatal conductance, and membrane stability. Alleles for improved root growth and distribution under water deficit exist in some japonica rice cultivars.     

Creation of new maize germplasm using alien introgression from <Emphasis Type="Italic">Zea mays</Emphasis> ssp. <Emphasis Type="Italic">mexicana</Emphasis>

Zea mays ssp. mexicana, an annual wild relative of maize, has many desirable characteristics for maize improvement. To transfer alien genetic germplasm into maize background, F₁ hybrids were generated by using Z. mays ssp. mexicana as the female parent and cultivated maize inbred line Ye515 as the male parent. Alien introgression lines, with a large range of genetic diversity, were produced by backcross and successive self-pollinations. A number of alien introgression lines with the predominant traits of cultivated maize were selected. Genomic in situ hybridization (GISH) proved that small chromosome segments of Z. mays ssp. mexicana had been integrated into the maize genome. Some outstanding alien introgression lines were evaluated in performance trials which showed 54.6% hybrids had grain yield greater than that of hybrid check Yedan12 which possessed 50% Ye515 parentage, and 17.1, 9.9% hybrids had grain yield competitive or greater than those of Nongda108 and Zheng958, which were elite commercial hybrids in China, respectively. The results indicated that some of the introgression lines had excellent agronomic traits and combining ability for maize cultivar, and demonstrated that Z. mays ssp. mexicana was a valuable source for maize breeding, and could be used to broaden and enrich the maize germplasm.     

Genetic diversity and population structure of wild and cultivated barley from West Asia and North Africa

Population structure and relationships within and among 185 accessions of wild (Hordeum vulgare ssp. spontaneum) and cultivated barley (H. v. ssp. vulgare) from five countries in the West Asia and North Africa (WANA) region were studied using 36 simple sequence repeat (SSR) markers. The accessions were divided into subspecies/origin (S/O)‐groups and marker results were analysed in relation to genetic diversity and genetic structure. Wild barley from WANA was found to be highly diverse. The landraces from different countries of the Near East showed genetic diversity that was nearly as high as the wild barley from the same country. Further analyses showed that wild barley from Palestine/Israel represented the group with the highest diversity and the most complex structure. However, this group was distantly related to the cultivated barley in WANA, while the wild barley from the rest of the WANA region was closely related to the cultivated WANA barley. The high diversity and the close relationship to the wild barley make the WANA landraces an interesting genetic resource for both conservation and exploitation.     

Development of drought‐tolerant breeding lines derived from Helianthus annuus × H. argophyllus interspecific crosses

Helianthus argophyllus is a wild species known as “silver sunflower”, which possesses several traits, including morphological traits that increase drought tolerance. Therefore, introgressions between chosen cultivated lines and two H. argophyllus accessions were made, and segregating generations were established. Important agronomic traits including single heading, high pollen fertility, silver canopy (indicating more cuticular wax), and content of cuticular waxes and oil were selected over six segregating generations. The resulting F₆ lines showed introgression of water saving traits, as they had lower excise leaf water loss, with comparable yield to standard checks. However, these F₆ lines were late maturing and showed poor flowering synchronization between the cultivated and introgressed lines. Introgressed line “D‐22” was particularly promising as a breeding line, with superior agronomic and drought resistance traits. This line had the potential to be used as an inbred parental line for introgression of drought resistance traits into elite sunflower germplasm. Combining ability analysis of the introgressed lines further showed their potential for heterosis breeding or to be used as parental lines in breeding programme.